“Eric Chewning, chief of staff to Defense Secretary Mark Esper, is stepping down at the end of the month, the latest in a series of high-profile Pentagon departures. Chewning, a former Army intelligence officer and combat veteran, managed the day-to-day operations in the Office of the Secretary of Defense. During his three-year tenure, he worked for four Pentagon chiefs.

“I’m grateful for Eric’s professionalism, judgment, and leadership over the last seven months as I moved into the Secretary of Defense role,” Esper said in a statement. “In an incredibly demanding job, Eric has been a source of calm and tireless work. He will be missed by all. We wish him all the best upon his return to the private sector.”

He’ll be replaced by Jen Stewart, the top Republican staffer on the House Armed Services Committee, according to a statement from Pentagon press secretary Alyssa Farah.

Stewart also served as a senior advisor to the Chairman of the Joint Chiefs of Staff, Gen. Joseph Dunford, and as the national security advisor to Speakers of the House Paul Ryan and John Boehner.

“I have known Jen for years and I’m excited to bring her into the Department,” Esper wrote. “Her deep expertise on national security issues will be a great addition to our team as we continue implementing the National Defense Strategy.”

Chewning’s move to leave the Pentagon comes on the heels of several other high-profile departures, including that of the director of Defense Advanced Research Projects Agency, or DARPA, the acting undersecretary for personnel and readiness and the assistant secretary for Asian and Pacific security affairs.